1. Division of Mathematics, Faculty of Science and Technology, Rajamangala University of Technology Krungthep, Bangkok, THAILAND
2. Division of Mathematics, Department of Science, Faculty of Science and Agricultural Technology, Rajamangala University of Technology Lanna Nan, Nan, THAILAND
3. Department of Mathematics, Faculty of Science and Technology, Rambhai Barni Rajabhat University, Chanthaburi, THAILAND